Integration of second-use of li-ion batteries in power generation

ABSTRACT

A method of managing second use batteries incudes communicating an external load demand to battery management modules (BMMs) of first use batteries and second use batteries; communicating, by each of the BMMs, the state of health (SoH) of the respective first or second use battery to the other BMMs; by the BMMs of the first use batteries with highest SoH, engaging the first use batteries to meet the external load demand, wherein the highest SoH is determined by the BMMs by ranking the SoH of each battery relative to the other batteries; and by the BMMs of the second use batteries, setting a discharge limit for each of the second use batteries based on the SoH of the respective second use battery, and controlling the second use batteries to supply currents not to exceed the discharge limits of the respective second use batteries to load-share with the first use batteries.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of Indian Application No:201811025958, filed on Jul. 11, 2018, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure relates to use of batteries in second useapplications, and more particularly to methods and systems for usingbatteries in second use applications.

BACKGROUND OF THE DISCLOSURE

Plug-in Hybrid Electric/Electric Vehicles (PHEV/EV) use batteriesdesigned to energize the vehicle to enable travel for a predetermineddistance. As the batteries age they are unable to satisfy the distancecriteria and are swapped for new batteries. Typically batteries degradedto 70-80% of their original capacity are swapped out of the vehicle.Used batteries may be recycled. However used batteries can also be usedin so called “second-use” applications, which are any applications inwhich swapped, or second use, batteries can be used. Second useapplications include power generation systems including commercial andindustrial stand-by applications, micro-grid and distributed powergeneration applications, among others.

Landfilling lithium ion batteries is illegal most places and noteconomic anywhere. Recycling them, at least given today's recyclingcapabilities, is effectively down-cycling and is relatively expensive.

Used batteries have lower energy density than new stationary-storagebatteries and will not last as long, since they are nearer the end oftheir lifecycle.

Most vexingly, EV batteries vary wildly. Not only do they have differentsizes, shapes, and performance characteristics when new, but they havebeen used differently, in different climates, under different stressors,in different cars. Batteries that have experienced differentenvironments and use cycles will have different degradationtrajectories.

However, degradation of second use batteries is of concern. Anotherconcern in power generation systems is the duty-cycle and fuelefficiency of electromechanical generators used to re-charge thebatteries or power the load. Better systems are needed to extend thelife of second use batteries and electromechanical generators whilesatisfying the load demands in a cost efficient manner.

SUMMARY

Embodiments of a method of using second use batteries are providedherein. In some embodiments, the method comprises communicating anexternal load demand to battery management modules (BMMs) of first usebatteries and second use batteries; communicating, by each of the BMMs,the state of health (SoH) of the respective first use battery or seconduse battery to the other BMMs; by the BMMs of the first use batterieswith highest SoH, engaging the first use batteries to meet the externalload demand, wherein the highest SoH is determined by the BMMs byranking the SoH of each battery relative to the other batteries; and bythe BMMs of the second use batteries, setting a discharge limit for eachof the second use batteries based on the SoH of the respective seconduse battery, and controlling the second use batteries to supply currentsnot to exceed the discharge limits of the respective second usebatteries to load-share with the first use batteries.

In some embodiments a battery management system is provided, comprising:a plurality of battery management modules (BMMs) communicatively coupledto each other to receive an indication of an external load demand and torespective first use batteries and second use batteries; each of theplurality of BMMs including a controller configured to transmit, to theother of the plurality of BMMs, a state of health (SoH) of a first usebattery or second use battery connected to the BMM; wherein thecontroller is configured to determine, from among a plurality of BMMsbased on respective states of health (SoH) of the batteries connected tothe BMMs, if the battery connected to the BMM has a higher SoH thanother batteries connected to the other of the plurality of BMMs and ifso, to engage the battery to supply power to the external load demand.

In some embodiments the method comprises determining a state of health(SoH) of a battery based on SoH parameters; comparing the SoH parametersto a plurality of SoH profiles to identify a SoH profile from theplurality of SoH profiles; estimating a remaining life of the batterybased on the SoH profile; determining, based on the remaining life ofthe battery, a depth of discharge (DOD) and state of charge (SoC) of thebattery; setting a threshold based on the remaining life of the battery;and characterizing the battery as a first use battery if a dischargetime, a discharge rate, the DOD, and the SoH of the battery exceed thethreshold and as a second use battery otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, corresponding reference characters indicatecorresponding parts throughout the several views. Unless statedotherwise the drawings are not proportional.

FIG. 1 is a block diagram of an embodiment of a power storage system;

FIG. 1A is a block diagram of a section of the embodiment of a powerstorage system of FIG. 1;

FIG. 2 is a flowchart of an embodiment of a method for determining if abattery is a second use battery;

FIG. 3 is a flowchart of an embodiment of a method for determining whento engage a second use battery;

FIG. 4 is a flowchart of an embodiment of a method for determining whento engage a generator set connected to the batteries;

FIG. 5 is a flowchart of an embodiment of a method for determining whento engage a generator set connected to the batteries to minimize thestart/stop frequency of the generator set;

FIG. 6 is a perspective view of the power system of FIG. 1;

FIG. 7 is a diagram representing the power system of FIG. 1; and

FIGS. 8-10 are flowcharts of an embodiment for determining cycling timefor second use batteries.

DETAILED DESCRIPTION

One object of the invention is to integrate second use batteries inpower systems to improve the overall cost effectiveness of the powersystems. Cost effectiveness improves by use of second use batteries,management of second use batteries to extend their useful life,management of electromechanical generators to extend their useful lifepower, and management of fuel provided to run the electromechanicalgenerators in novel ways described below.

Integration of first and second use batteries can occur under differentcircumstances. For example, in a stationary application, a customer maychoose to upgrade an existing system by adding newer batteries andinverters to existing ones that are partially degraded. Or perhaps thebatteries resided in a location that flooded and some batteries must bereplaced but not others. Or, if the batteries are semi-portable modularunits (e.g. rental or military markets), the containers could getmix-and-matched and each may have aged differently due to use the caseor environmental conditions to which they were exposed. The existingbatteries that were not initially used in electric vehicle applicationsare considered second use anyway if they their capacity has degraded to70-80% of the original capacity.

Battery life or remaining life is a measure of battery performance andlongevity, which can be quantified in several ways: as run time on afull charge, as estimated by a manufacturer in ampere-hours, or as thenumber of charge cycles until the end of useful life. For lithium-ionbatteries cycling, elevated temperature, and aging decrease performanceover time.

Discharge time is the Ah rating divided by the current, which is basedon the load. The charge time depends on the battery chemistry and thecharge current. For NiMh, for example, the charge time is typically 10%of the Ah rating for 10 hours. Li-Ion can typically be charged at theC/1 rate to about 75% capacity and then at a reduced rate for thebalance.

State of health (SoH) is a figure of merit of the condition of a batterycompared to its ideal conditions measured as percent points. SoH can beused to estimate the battery's useful lifetime or remaining life in aparticular application. Capacity is a health indicator. Although abattery should deliver 100% of specified capacity during the first yearof service, it is common to see lower than specified capacities.Internal resistance and self-discharge may be used as health indicatorsin combination with capacity. Voltage, ability to accept a charge, andthe number of charge/discharge cycles can also be used by a batterymanagement module or system to derive SoH. Arbitrary weights can beapplied to each parameter's point value. The SoH threshold below whichan application deems a particular battery unsuitable is arbitrary. Anapplication may accept a battery with a SoH of 50% and above, while amore critical application may only accept batteries with a SoH of 90%and above.

Cycling may reduce the original capacity up to more than 20%. State ofCharge (SOC)(%) represents the present battery capacity relative to theavailable capacity, which can be the original capacity or the degradedcapacity. SOC is generally calculated using current integration todetermine the change in battery capacity over time. Depth of Discharge(DOD)(%) represents the percentage of the present battery capacity thathas been discharged. A discharge to at least 80% DOD is referred to as adeep discharge.

Second use batteries, for example second use Li-ion batteries, can beintegrated into power systems for commercial/industrial stand-byapplications or in micro-grid/distributed power generation applicationsin novel integrating ways are described below with reference to specificembodiments in connection with the figures. Batteries may be diagnosedbefore they are added to the system to determine if they are first orsecond use batteries. Diagnosis may determine the SoH and DOD of theadded battery and is performed because the origin and use history of thebattery being added to the system may be unknown. Second use batteriesare used to supplement first use battery capacity. In some variations,thresholds are used to minimize cycling of the second use batteriesthereby extending their life. When the aggregate (first and second usebatteries) battery capacity is insufficient to satisfy a total demand,power generators are engaged to add electrical energy to the system,thus meeting the external load demand and recharging the batteries. Insome variations, thresholds are used to minimize cycling of the powergenerators thereby extending their life.

Several practices can mitigate degradation of Li-ion batteries.Partial-discharge cycles, in the order of less than 30% of batterycapacity, can extend battery life. Keeping the battery fully charged canshorten its life. Charging below 0° C. or above 40° C. can decreasebattery life, as can high charge and discharge currents and very deepdischarges. Charging at a constant rate and then reducing the rate whenthe voltage reaches a float voltage increases battery life. The floatvoltage can be set to prevent charging the batteries to 100% capacity.

Second use Li-ion batteries may be paralleled with newer Li-ionbatteries. It should be noted that “battery” refers to any combinationof battery cells. A battery also refers to a battery pack or a rackmounted battery pack. The bi-directional inverter coupled to eachbattery effects charging and discharging. Bi-directional inverters aresized based on the state of health and charging/discharge thresholddetermined.

In some embodiments, the power system comprises driven power sourcesthat supply three-phase power and a power transmission network totransfer power from the power sources to the load. The load may be adevice that requires uninterrupted power to operate, for example lights,motors, power supplies and appliances such as refrigerators. The drivenpower sources, referred to as gensets, comprise a fuel consuming enginerotating an electrical machine configured to induce electrical energyand generally referred to as a generator or alternator.

The charging/discharging cycle of the batteries is triggered to rechargethe batteries and, if necessary, to supply electrical energy to theload. In the latter case, the gensets must be capable of satisfying theexternal load demand plus the charging demand. As indicated previously,Li-ion batteries are preferably charged at a fast rate when they arebelow 30% DOD and at a slow rate as they approach full charge. The slowrate may be constant or decrease as the battery approaches full charge.Charging at the slow rate extends battery life. In some examples, thegensets are engaged to prevent that the batteries are discharged morethan a predetermined DOD.

In some variations, a discharge threshold is set to determine when toengage the gensets. In one example, the discharge threshold is comparedto the aggregate SOC of a first group of batteries, comprising onlyfirst use batteries, and when the aggregate SOC equals the dischargethreshold the gensets begin to operate to add electrical energy to thesystem. The electrical energy supplied by the gensets should exceed theexternal load demand, with the excess energy provided to charge thebatteries.

In some variations, battery selection to power the external loaddifferentiates on charge/discharge rate for the purpose of preservingthe SoH of the second use batteries. In one example, first usebatteries, or batteries with SoH higher than a SoH threshold, areengaged to supply energy to compensate for transient load conditions, inwhich either the load increases (or decreases) rapidly or by an amountgreater than a threshold, and second use batteries are only engaged insteady state load conditions. By engaging the second use batteries onlyin steady state load conditions the rate of discharge can be relativelylow, thereby extending the life of the second use batteries beyond whatit would be if the rate of discharge were higher. Furthermore,discharging second use batteries at a low discharge rate reducescycling, which also extends their life. In another example, second usebatteries are sufficiently large that they are used with first usebatteries to supply energy to compensate for transient load conditions.For instance, if a second use battery has a capacity that is a multipleof a first use battery, e.g. 5×, then even at a low discharge rate (as apercent of capacity) the second use battery may output as much currentas the first use battery.

First and second use batteries may be engaged in different modes ofoperation to achieve the objects of the invention. IN A FIRST MODE OFOPERATION, first and second use batteries are engaged to supply theexternal load. In one example, the first mode of operation is employedwhen the external load is low enough that operating the gensets, or anadditional one, would be fuel inefficient. For example, the first groupof batteries may be engaged when the external load is less than aninefficiency threshold based of the capacity of a genset. Theinefficiency threshold may be, for example, 30%. Thus if the externalload is less than the inefficiency threshold, or less than an integerplus the inefficiency threshold, then the first use batteries areengaged to avoid inefficient use of a genset or avoid use of anadditional genset, thus saving fuel. In the first mode of operation theexternal load is in a steady state.

IN A SECOND MODE OF OPERATION, first use batteries are engaged to supplythe external load when the external load is transient and increasing,during which time the second use batteries may or may not be engaged.The first use batteries may supplement power from the gensets as theload increases. Increasing load without batteries to compensate causesthe gensets to slow down, perhaps into an inefficient area. Adding thecapacity of one or more first use batteries maintains the gensets in theefficient area of operation. As the gensets speed-up to absorb theadditional load the first use batteries may gradually supply less energyand eventually disengage. Thusly, the faster energy supply response ofthe first use batteries helps improve the fuel efficiency of thegensets. If the second use batteries were engaged, they may remainengaged but the current supplied by them will be maintained at or belowa discharge rate limit selected to preserve the SoH of the batteries, asdescribed below.

IN A THIRD MODE OF OPERATION, first use batteries are engaged to supplythe external load when the external load is transient and decreasing,during which time the second use batteries may or may not be engaged.The first use batteries may supplement power from the gensets as theload decreases, to enable one or more gensets to be disengaged. Thefirst use batteries compensate for the reduction caused by disengagementof one or more gensets.

The gensets must be controlled. In one variation, controlling thegensets includes estimating the conditions for running the engines tocharge the batteries and supply the external load, considering fueleconomy, the life to overhaul of the gensets and reducing the start/stopfrequencies to increase the life to overhaul, and estimating based onthe historic duty cycle of the gensets charging the batteries accordingto an anticipated load.

IN A FOURTH MODE OF OPERATION, a master controller provides signals tothe gensets, to engage the gensets when the aggregate SOC of the firstuse batteries is less than or equal to the discharge threshold. Thegensets may be engaged, assuming the external load demand remains, untilthe aggregate SOC rises to 90%.

IN A FIFTH MODE OF OPERATION, the gensets are engaged to supply energyto the external load and charging of the first and second use batteriesincreases the load on the gensets to cause them to operate in a moreefficient range. The fuel efficient rate may be based on a fuel map. Forexample, it may be inefficient for the combustion engines of the gensetsto operate below 30% load. Charging of the batteries may suffice toincrease the load from below 30% to above 30%. A genset may bedisengaged to increase the load on the remaining gensets. In that caseit may be appropriate to stop charging the first use batteries to enabledisengaging a genset so as to enable the remaining gensets to supply theexternal load, if charging the first use batteries would exceed thecapacity of the remaining gensets. In some embodiments, a batterymanagement module provides a signal to the gensets to engage the gensetswhen the aggregate SoH is 20%. The gensets are engaged until the SoHrises to 90%.

The foregoing embodiments, variations thereof, and examples, andadditional ones, will now be described with reference to the figures.FIG. 1 is a block diagram of an embodiment of a power system 20 whichmay receive resources 22 such as electrical energy, from a power grid orrenewable resources, and fuel to run electromechanical generators, topower a load 24. Power system 20 includes several batteries 32-38 andinverters 42-48. Each battery is communicatively coupled to a batterymanagement module (BMM) 50 to supply DC electricity to a DC bus. BMM 50comprises (not shown) a processor 96 and memory 98 comprising processinginstructions structured to control inverters 42-48 to charge ordischarge batteries 32-38. In combination these components of powersystem 20 may be referred to as the energy storage subsystem 54. BMMscan be housed individually or together to form a battery managementsystem 51. Such processing instructions comprise instructions configuredto implement the methods described herein, including at least in partthe methods described with reference to FIGS. 2-5 and 8-10.

Power system 20 also includes several electromechanical generators, alsoreferred to as driven power sources and gensets 62-68 communicativelycoupled to a master controller 70 structured to cause gensets 62-68, orany of them, to operate so as to supply AC energy to an AC bus 72. Incombination these components of power system 20 may be referred to asthe AC subsystem 74. AC subsystem 74 may comprise generator sets,transfer switches, digital master controls complete with integratedswitchgear and remote monitoring controls in a single integrated controlsystem that can directly operate the engine fuel system in conjunctionwith an engine control unit where appropriate, directly control thealternator excitation system and provide other control functions thatincrease reliability. Operating over a broad bus voltage and frequencyoperating range, the generator set governing controls are temperaturedynamic, automatically adjusting governing characteristics to accountfor changes in engine operating temperature. This enables the system tosynchronize even in the event of instability on the bus or abnormalfrequency conditions system. Digital paralleling only requires onedigital master controller, regardless of the number of paralleledgenerator sets, reduces the ‘footprint’ of the control modules of eachgenerator set in addition to centralizing information and control intoone input/output device. Additional details pertaining to a mastercontroller, bi-directional inverters, and gensets are disclosed in U.S.Pat. No. 9,780,567, issued Oct. 3, 2017, and U.S. Pat. No. 812,866,issued Nov. 7, 2017, which are incorporated by reference herein in theirentirety.

A smart inverter 80 may be provided to couple DC bus 52 to a transformer84 and a transfer switch 86 to supply energy from DC bus 52 to theutility grid. DC bus 52 may also be coupled directly to DC loads 24.Inverters 42-48 may be coupled to AC bus 72 thus coupled to gensets62-68 in a parallel arrangement. As used herein an inverter is a devicethat is used to convert a DC voltage to an AC voltage, and a converteris a device that is used to convert AC voltage to DC voltage. Invertersinclude controls and power modules, as is well known in the art, whichutilize pulse-width-modulation (PWM) logic to control the gates of powerdevices to generate AC voltages of desired amplitude and frequency.Converters may be static, comprising rectifiers, or dynamic, comprisingpower modules gated to generate DC voltages of desired amplitude.

As described below, battery management logic and generator managementlogic are configured to control operation of the batteries, whichinclude first and second use batteries, and the gensets, to satisfy theobjects of the invention. The term “logic” as used herein includessoftware and/or firmware comprising processing instructions executing onone or more programmable processors, application-specific integratedcircuits, field-programmable gate arrays, digital signal processors,hardwired logic, or combinations thereof, which may referred to as“controllers”. Therefore, in accordance with the embodiments, variouslogic may be implemented in any appropriate fashion and would remain inaccordance with the embodiments herein disclosed. A non-transitorymachine-readable medium comprising logic can additionally be consideredto be embodied within any tangible form of a computer-readable carrier,such as solid-state memory, magnetic disk, and optical disk containingan appropriate set of computer instructions and data structures thatwould cause a processor to carry out the techniques described herein. Anon-transitory computer-readable medium, or memory, may include randomaccess memory (RAM), read-only memory (ROM), erasable programmableread-only memory (e.g., EPROM, EEPROM, or Flash memory), or any othertangible medium capable of storing information.

FIG. 1A is a block diagram of a portion of the embodiment of powersystem 20 described with reference to FIG. 1. As shown in FIG. 1A, anexternal load demand is communicated to BMMs 50 of first use batteries35 and second use batteries 39. In the present example, batteries 32 and34 are designated as first use batteries and batteries 36 and 38 aredesignated as second use batteries 39. The designation is illustrative.A battery 33 is also shown, illustratively a replacement battery.Battery 33 could also be an additional battery, in which case a BMM 50may be added to monitor it and conduct a battery diagnostics test todetermine its SoH and characterize it as a first use or second usebattery.

In some variations, a method of using the second use batteries includesdetermining the predefined battery discharging time period. Thedetermination is made by calculating the peak-power and continuous powerdemand the batteries can support, calculating the power threshold of thebatteries to reduce the charge/discharge cycling of the batteries, andcontrolling the cycling without active temperature control and within apredetermined temperature range. In one example, the power threshold isdetermined to set a life-extending discharge rate limit and minimizecycling.

In some variations, a monitor system controls bi-directional invertersto transmit power from second use Li-ion batteries to the load untilwhen doing so would exceed the determined power threshold. In somevariations, a monitor system controls bi-directional inverters totransmit power from second use Li-ion batteries to the load until whendoing so would exceed the determined power threshold. In othervariations, a distributed control system is employed to controlbi-directional inverters to transmit power from second use Li-ionbatteries to the load until when doing so would exceed the determinedpower threshold. In the distributed system BMMs control the inverters.Each BMM receives demand information and information relating to gensetuse and any other data the BMM requires to determine when to engage arespective battery.

In various embodiments, paralleling architecture enables second use andnewer Li-ion batteries to support different continuous and peak-loaddemands, and control the charge/discharge rate according to the demandload and the power threshold set for the second-use and newer Li-ionbatteries. The paralleling architecture prevents cell chargeequalization and enables more accurate SOC predictions. Paralleling willprolong the battery life of both second use and first use Li-ionbatteries based on the C-rates and cycling control, will enable moreaccurate temperature control of second use and first use Li-ionbatteries and reduce the parasitic load of active thermal management.

Generally, using a SoH threshold, the exemplary method comprisesdetermining whether a battery is a first or second use battery. If theSoH is greater than the SoH threshold the battery is a first use batteryand is a second use battery otherwise. Even more generally, the SoH canbe based on the SOC only, in which case an SOC threshold is used todistinguish between first and second use batteries. The batteries arediagnosed so the power system knows how many first and second usebatteries there are and also knows the amount of energy available fromthem when they are fully charged. The power system may anticipate demandwithout a master load manager. Energy storage is modular. The energystorage modules are integrated and the load demand is communicatedbetween them. Communications may comprise comparing the SoH of a moduleto the SoH of the other modules. Modules can be grouped into a firstgroup comprising first use batteries and a second group comprisingsecond use batteries. The SoH comparisons identify the modules with thehigher SoH. In one example the modules are ordered based on SoH. Thebatteries from the first group with the highest SoH will be used first.When the SOC of batteries from the first group falls below a threshold,batteries from the second group are connected to supply energy. If loaddemand continues, batteries from the first and second groups willdischarge sufficiently to trigger a charging cycle. In one variation,only data from the first group is used to trigger a charging cycle.Therefore data from the first group is used to engage the second groupand to generate power without using data about the second group.

FIG. 2 is a flowchart 100 of an embodiment of a method to determine if abattery is a second use battery. The method addresses the fact that thehistory of batteries may not be known. If the history is known then thehealth may be determined from the history data. At 102, the health ofthe second use battery is diagnosed to characterize its performance. At104, the health is compared to predefined health scenarios and one ofthe scenarios is selected based on fit. Fit may be determined bydetermining an error based on the comparisons to the different scenariosand selecting the scenario with the least error.

At 106, depth of discharge and state of charge are determined based onthe scenario selected from the fitting step.

At 108, depth of discharge and state of charge are compared tothresholds and a determination is based on the comparison. If, at 110,the parameters exceed the thresholds, then the battery is deemed a firstuse battery. If, at 112, the parameters do not exceed the thresholds,then the battery is deemed a second use battery.

FIG. 3 is a flowchart 140 of an embodiment of a method for determiningwhether to discharge a first use or a second use battery to supply theload. At 142, the capacity of the second use battery is diagnosed if itis unknown. At 144, a power threshold is determined based on thecapacity. At 146, the demand is compared to the power threshold. At 148,if demand exceeds the power threshold, then power is transferred fromthe first use battery to the load. Transferring power discharges thefirst use battery. At 150, if demand does not exceed the powerthreshold, then power is transferred from the second use battery to theload. The power threshold may be determined to ensure that the seconduse battery is not discharged quickly, which would occur if demandexceeds the power threshold, thereby extending the life of the seconduse battery.

FIG. 4 is a flowchart 180 of an embodiment of a method for discharging asecond use battery under steady-state or transient conditions and fordetermining when to engage the gensets. At 182, the state of the loaddemand is determined. The load demand state can be determined byanalyzing the power usage, duty cycle, and other historical parameters,to characterize demand by the load over time and distinguish transientfrom steady-state demand. Generally, steady-state demand is demand thatrequires voltage and current within a band for an observation period,the width of the band determinable based on the historical data. Ifdemand is not steady-state it is transient. Generally, transient demandis demand that requires voltage and current that fluctuate outside aband for an observation period. Transient demand may include demand thatis increasing or decreasing over the observation period. The outcome isa determination of whether the load is in a transient state orsteady-state.

At 184, the load demand is estimated based on the classification of thestate of the load.

Based on the estimated load demand, which is based on the state, at 186,various parameters related to battery discharge controls are determined.These may include discharge time, discharge rate, energy and power out.Then, at 188, a decision is made regarding the energy and power that isto be discharged to meet the load demand. The decision may becommunicated between the batteries, e.g. the BMM module corresponding tothe battery, and the control modules associated with each genset.

At 194, the first use batteries with highest SOH and SOC are identifiedto supply the energy and power.

At 196, the first use batteries with highest SOH and SOC are identifiedto supply the energy and power.

At 198, the second use batteries with highest SOH and SOC are identifiedto supply the energy and power in a load sharing arrangement when theSOC of the first use batteries falls below a threshold. Thereby firstand second use batteries supply the energy and power to the load.

Meanwhile, at 200, the aggregate SOC of the batteries is compared to atotal load threshold equal to the aggregate battery recharge load plusthe load demand. The battery recharge load is the load that must besatisfied to recharge the batteries to a desirable SOC, which mayapproximate the capacity of each battery. The total load thresholdserves to determine when the gensets may be engaged to supply the loadand also recharge the batteries. Of course not all the batteries must berecharged simultaneously.

At 202, the gensets are started when the total load threshold exceedsthe aggregate SOC.

FIG. 5 is a flowchart of an embodiment of a method 220 for determiningwhen to engage a generator set connected to the batteries to minimizethe start/stop frequency of the generator set. The method includes:

At 222, the method begins with aggregation of SoC from all the batteryracks to set the load demand for starting the Genset. Aggregation may beperformed by a battery module or the digital master controller. The loaddemand for starting the Gensets may represent, for a given system, theproportion of the load demand which cannot be serviced by the batterieswithout operating them at disfavored SoH or SoC.

At 224, the method continues with setting thresholds forcharge/discharge rates to preserve the SoH of second life batteries.Thresholds may also be set before aggregation of SoCs.

At 226, the method continues with estimating conditions for running theengines of the Gensets at higher loads for charging the batteries. Theconditions may include the charge/discharge rates of the second lifebatteries, to enhance their longevity. The aggregated SoC is used todetermine when the batteries are low and need charging, and the chargerates are used to add enough load to the Gensets to charge batteries atthe appropriate rate.

At 228, the frequency of engine start and stop for recharging the secondlife batteries is reduced, as a result of increasing the life of thesecond use batteries as described above, therefore not requiring as manystarts as would otherwise be required.

FIGS. 8-10 are flowcharts of an embodiment for determining cycling timefor second use batteries.

The scope of the invention is to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” Moreover, where a phrase similar to “at least oneof A, B, or C” is used in the claims, it is intended that the phrase beinterpreted to mean that A alone may be present in an embodiment, Balone may be present in an embodiment, C alone may be present in anembodiment, or that any combination of the elements A, B or C may bepresent in a single embodiment; for example, A and B, A and C, B and C,or A and B and C.

In the detailed description herein, references to “one embodiment,” “anembodiment,” “an example embodiment,” etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment.

As used herein, the terms “comprises,” “comprising,” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

The embodiments and examples described above may be further modifiedwithin the spirit and scope of this disclosure. This application coversany variations, uses, or adaptations of the invention within the scopeof the claims.

What is claimed is:
 1. A method of using second use batteries, themethod comprising: communicating an external load demand to batterymanagement modules (BMMs) of first use batteries and second usebatteries; communicating, by each of the BMMs, the state of health (SoH)of the respective first use battery or second use battery to the otherBMMs; by the BMMs of the first use batteries with highest SoH, engagingthe first use batteries to meet the external load demand, wherein thehighest SoH is determined by the BMMs by ranking the SoH of each batteryrelative to the other batteries; and by the BMMs of the second usebatteries, setting a discharge limit for each of the second usebatteries based on the SoH of the respective second use battery, andcontrolling the second use batteries to supply currents not to exceedthe discharge limits of the respective second use batteries toload-share with the first use batteries.
 2. The method of claim 1,wherein controlling the second use batteries to supply currents not toexceed the discharge limits of the respective second use batteriescomprises the BMMs of the second use batteries engaging the second usebatteries responsive to determining that the engaged first use batteriesreached an aggregate state of charge below a threshold.
 3. The method ofclaim 1, further comprising, by a BMM connected to an additional orreplacement battery, conducting a battery diagnostics test to determinethe SoH of the additional or replacement battery, and characterizing theadditional or replacement battery as a first use battery or a second usebattery.
 4. The method of claim 3, further comprising, charging thefirst use batteries with a generator-set coupled to power the externalload when an efficiency of the generator-set exceeds an efficiencythreshold and not otherwise.
 5. The method of claim 4, furthercomprising disengaging the generator-set when the efficiency is lessthan the efficiency threshold irrespective of a state of charge of thesecond use batteries.
 6. The method of claim 5, further comprisingengaging the generator-set to power the external load when the powersupplied by the first use batteries exceeds an amount of power which,when provided by the generator-set, would cause the generator-set tooperate at an efficiency greater than the efficiency threshold.
 7. Themethod of claim 6, wherein engaging the generator-set is performedirrespective of the state of charge of the second use batteries.
 8. Themethod of claim 4, wherein charging the first use batteries with agenerator-set coupled to power the external load when an efficiency ofthe generator-set exceeds an efficiency threshold and not otherwise isperformed when the efficiency of each generator-set coupled to power theexternal load is above the efficiency threshold.
 9. The method of claim4, wherein engaging the first use batteries to meet the external loaddemand comprises coupling the first use batteries and the generator-setto load-share, wherein load-share comprises supplying an amount of powerto the external load, jointly by the first use batteries and thegenerator set, equal to the external load demand.
 10. The method ofclaim 9, wherein coupling the generator-set to load-share with the firstuse batteries is performed irrespective of a state of charge of thesecond use batteries.
 11. The method of claim 1, wherein engaging thefirst use batteries to meet the external load demand comprises couplingthe first use batteries to supply an amount of power to the externalload sufficient to prevent operation of a generator-set to supply powerto the external load if the generator-set would thus operate below anefficiency threshold.
 12. The method of claim 1, wherein engaging thefirst use batteries to meet the external load demand comprises couplingthe first use batteries to supply an amount of power to the externalload sufficient to prevent operation of a generator-set to supply powerto the external load if the generator-set would thus operate below anefficiency threshold.
 13. The method of claim 1, wherein load-sharingcomprises engaging the second use batteries and the first use batteriesto supply an amount of power to the external load equal to the externalload demand.
 14. A battery management system comprising: a plurality ofbattery management modules (BMMs) communicatively coupled to each otherto receive an indication of an external load demand and to respectivefirst use batteries and second use batteries; each of the plurality ofBMMs including a controller configured to transmit, to the other of theplurality of BMMs, a state of health (SoH) of a first use battery orsecond use battery connected to the BMM; wherein the controller isconfigured to determine, from among a plurality of BMMs based onrespective states of health (SoH) of the batteries connected to theBMMs, if the battery connected to the BMM has a higher SoH than otherbatteries connected to the other of the plurality of BMMs and if so, toengage the battery to supply power to the external load demand.
 15. Thebattery management system of claim 14, wherein the controllers connectedto the second use batteries are configured to set discharge limits foreach of the second use batteries based on the SoH of the respectivesecond use battery, and are configured to control the second usebatteries to supply currents not to exceed the discharge limits of therespective second use batteries to load-share with the first usebatteries.
 16. The battery management system of claim 15, wherein tocontrol the second use batteries to supply currents not to exceed thedischarge limits of the respective second use batteries the controllersare configured to engage the second use batteries responsive todetermining that the engaged first use batteries reached an aggregatestate of charge below a threshold.
 17. The battery management system ofclaim 14, further comprising, by a BMM connected to an additional orreplacement battery, conducting a battery diagnostics test to determinethe SoH of the additional or replacement battery, and characterizing theadditional or replacement battery as a first use battery or a second usebattery.
 18. A battery management module (BMM) comprising: a controllerconfigured to receive an external load demand and transmit a state ofhealth (SoH) of a first use battery or second use battery connected tothe BMM; wherein the controller is configured to determine, from among aplurality of BMMs based on respective states of health (SoH) of thebatteries connected to the BMMs, if the battery connected to the BMM hasa higher SoH than other batteries connected to the other of theplurality of BMMs and if so, to engage the battery to supply power tothe external load demand.
 19. (canceled)
 20. The method of claim 2,further comprising, by a BMM connected to an additional or replacementbattery, conducting a battery diagnostics test to determine the SoH ofthe additional or replacement battery, and characterizing the additionalor replacement battery as a first use battery or a second use battery.21. The battery management system of claim 16, further comprising, by aBMM connected to an additional or replacement battery, conducting abattery diagnostics test to determine the SoH of the additional orreplacement battery, and characterizing the additional or replacementbattery as a first use battery or a second use battery.